1. Field of the Invention
This invention relates to an improvement in a process for producing acrylamide by reacting acrylonitrile with water in the presence of a copper-based catalyst.
2. Description of the Prior Art
Acrylamide has been used in acrylamide polymers which are useful as papermaking chemicals, flocculents, oil recovery additives, soil hardeners, etc., and also has found extensive use as a comonomer for other polymers. Early production of acrylamide for these uses was by the so-called sulfuric acid process. Recently, a catalytic hydration process which comprises reacting acrylonitrile with water in the presence of a copper-based catalyst was developed and has now superseded the sulfuric acid process in industrial production.
Various copper-based catalysts to be described hereinbelow are used in a liquid phase fixed bed or suspended bed in the hydration of acrylonitrile. In either case, however, the catalysts undergo degradation and lose activity with the lapse of time. In an attempt to remedy this defect, there have been proposed many methods which include the pretreatment of the starting acrylonitrile with an acidic aqueous solution or a cation exchange resin (Japanese Laid-Open Patent Publications Nos. 29154/1975 and 108916/1977), the addition of salts such as NaCl to the acrylonitrile hydration system (U.S. Pat. No. 3,869,511), and the regeneration of the degraded catalyst by a reducing treatment (U.S. Pat. No. 3,645,913).
These prior methods are effective, and as required, some of them may be used in combination as a series of improved methods. In order to increase the utility of this new manufacturing process, it has been desired to develop a more effective method for maintaining the activity of copper-based catalysts.